1. Field of the Invention
The present invention relates to a solid catalyst component for olefin polymerization. More particularly, the present invention relates to a novel catalyst component used to produce granular olefinic thermoplastic elastomers and olefinic elastomers. Among various thermoplastic elastomers and elastomers, olefinic thermoplastic elastomers and olefinic elastomers, because of their excellent thermal resistance, ozone resistance and color stability, are mainly used in the fields of automobiles, household electric appliances and architecture.
2. Description of the Prior Art
Hitherto, the olefinic thermoplastic elastomers are produced by separately producing polypropylene or other olefinic resins and olefinic copolymeric rubbers (e.g. ethylene/propylene rubbers) in advance and then blending two these components. However, the olefinic copolymeric rubbers are generally produced by solution polymerization, so that this method is disadvantageous in terms of the cost. Also, strong kneading is necessary to blend with the olefinic resins, so that large quantities of energy is necessary, and therefore this method is disadvantageous in terms of the manufacturing cost. This is a well-known fact.
A method of directly producing the foregoing thermoplastic elastomers under particular conditions according to slurry-phase two-stage polymerization is proposed by JP-A-No. 55-80418, JP-A-No. 57-61012, etc. Also, in these methods, the ethylene/propylene random copolymer is dissolved in large amounts in a solvent, so that the viscosity of the system increases to make the removal of the polymerization heat difficult and markedly promote adhesion of the polymer particles. As a result, there is a problem of stable production being difficult. In order to solve this problem, it is proposed to carry out the random copolymerization of ethylene with propylene at a very low temperature below 30.degree. C. This method, however, has problems that the catalytic activity lowers, and that a large-sized refrigerator is necessary to remove the polymerization heat, which is disadvantageous economically.
Further, a method of producing the thermoplastic elastomers by gas-phase two-stage polymerization is proposed by JP-A-No. 59-105008. In this method, a reduction in the adhesive power of the polymer particles is tried by using inorganic oxides (e.g. silica gel) as a carrier for solid catalyst components, but the improvement effect of this method is still unsatisfactory.
The olefinic elastomers are generally produced by solution polymerization. This solution polymerization requires many steps including a step for recovering unreacted monomers, a step for removing ashes, a step for stripping, etc. And also, the formed polymer is in solution in the system, so that the viscosity of the system is high and stirring and heat removal are difficult, which is very disadvantageous in terms of the manufacturing cost.
In order to solve this problem, a method of producing the ethylene/propylene random copolymer by slurry polymerization in a liquid propylene is proposed by JP-A-No. 59-71306. In this method, an improvement in the productivity is observed, but the polymerization needs to be carried out at a very low temperature below 40.degree. C., so that the catalytic activity lowers and also a large-sized refrigerator is necessary to remove the polymerization heat, which is disadvantageous from the industrial point of view.
Further, a method of directly producing the thermoplastic elastomers by gas-phase polymerization is proposed by JP-A-No. 59-230011. Also, in this method, in order to prevent the adhesion of the polymer particles thereby to carry out the gas-phase polymerization stably, the polymerization needs to be carried out at a low temperature and in a state wherein the monomer is diluted with a very large volume of inert gases such as nitrogen, etc. This method has problems of reducing the productivity and causing disadvantages in terms of industrial production.
In view of the situation like this, a problem to be solved by the present invention, i.e. an object of the present invention is to provide a novel solid catalyst component which makes it possible to improve the conventional technique of separately producing polypropylene and olefinic copolymeric rubbers (e.g. ethylene/propylene rubbers) in advance and then blending two these components, a method of producing the thermoplastic elastomers by slurry-phase two-stage polymerization at a low temperature, a technique of producing the thermoplastic elastomers by gas-phase two-stage polymerization using catalysts with inorganic oxides as a carrier, a technique of producing the olefinic elastomers by solution polymerization, a technique of producing the olefinic elastomers by slurry polymerization at a low temperature, and a technique of producing the olefinic elastomers by gas-phase polymerization at a low temperature and at a low monomer concentration, and also produce the granular olefinic thermoplastic elastomers and olefinic elastomers which are more superior in the performances by gas-phase polymerization.
In polymers containing a large amount of low crystalline polymers (e.g. ethylene/propylene rubbers), the adhesive power of the polymer particles is generally so markedly large that it is difficult to carry out the gas-phase polymerization stably.
That is, as a reactor for the gas-phase polymerization of .alpha.-olefins, stirring/mixing vessel-type reactors, fluidized bed-type reactors, fluidized bed-type reactors equipped with a stirrer, etc. are proposed. When, however, the adhesive power of the polymer particles increases, reactors wherein stirring is to be carried out requires extremely a large power in order to keep a definite number of stirrings, so that the design of the equipments is accompanied by great difficulty. Also, in such cases, uniform mixing becomes difficult to attain, so that the distribution of high-temperature regions in the system is localized. As a result, a part of the polymers turns lump, and these lumps break the stirrer and thermometer in the reactor and make it difficult to draw the polymer particles from the reactor through a pipe.
On the other hand, in reactors wherein the polymerization is carried out in a fluidized state, the slagging phenomenon owing to the unreacted monomers becomes easy to occur, and as a result, the amount of the polymer particles scattered to the gas-circulation lines remarkably increases to cause adhesion of the particles to the lines and clogging of the lines with the particles.
Also, in such cases, uniform mixing is so difficult that there occurs a problem that a part of the polymers turns lump.
Further, when the adhesive power of the polymer particles is large, clogging of pipes through which the polymer particles are sent becomes easy to occur. Also, since bridging occurs at the lower part of the cyclones or inside the hoppers, there occurs a problem that it becomes difficult to draw the polymer particles stably from the cyclones or hoppers.
Consequently, although the gas-phase polymerization has an advantage of using no liquid medium which dissolves the low crystalline polymers, it is considered to be very difficult, in reality, to produce polymers containing the low crystalline polymers in large amounts.
Further, in the improved gas-phase polymerization, removal of the catalyst residues is not substantially carried out, so that the catalyst system used needs to be one highly improved in the polymerization activity.
The present inventors have extensively studied to solve the foregoing problems, and as a result, have found a solid catalyst component which enables granular olefinic thermoplastic elastomers and olefinic elastomers having excellent performances to be obtained efficiently by gas-phase polymerization. The present inventors thus attained to the present invention.